By rights, no one should care much about Target 2. It is an arcane piece of the plumbing in the eurozone that pushes euros around the system. It stands for Trans-European Automated Real-time Gross settlement.

The chart above, though, shows why it could start to matter if Greece (or even other countries) leaves the eurozone. Germany's banks, through the Bundesbank, have €640bn (£510bn) of balances in the system. Greece, for instance, has €107bn that it needs to pay back through the system, according to the last disclosed figures. Bank analysts at UBS point out that Spain, Italy, Ireland and Portugal are the other major debtors in Target 2.

The UBS analysts reckon that the €640bn that Germany has in credit could rise to €1tn as problems in the peripheral nations rise.

"This is a powerful incentive for the creditor nations to work on keeping the monetary union together," the UBS analysts said.

They argue that the eurobonds are becoming increasingly necessary and that pressure on Spain is mounting as the country's banks weaken.

Crucially, they argue that the Spanish bank recapitalisation must be "domestically driven and financed". There is speculation that Spains wants to pump €19bn into troubled Bankia by issuing government bonds that can be exchanged for euros at the European Central Bank, although the picture is far from clear about exactly what Spain intends to do and what the ECB's view is.

Ownership of Spanish government bonds. Source: UBS

The UBS analysts, though, say: "Our view is that resolving Spain's banking system will prove a turning point for the euro-area – for better or worse." They argue that the European Stability Mechanism should not be used to inject the fresh cash – as mooted by the European commission on Wednesday – just to prevent Spain being bailed out by the EU and International Monetary Fund. And, while Spain's banks need to take provisions for the losses on property, they are also becoming more difficult to ringfence from the wider economy because the domestic banks are buying up the government's debt.